Today's Climate Change Proves Much Faster Than Changes in Past 65 Million Years

The climate is changing at a pace that's far faster than anything seen in 65 million years, a report out of Stanford University says.

The amount of global temperature increase and the short time over which it's occurred create a change in velocity that outstrips previous periods of warming or cooling, the scientists said in research published in today's Science.

If global temperatures rise 1.5 degrees Celsius over the next century, the rate will be about 10 times faster than what's been seen before, said Christopher Field, one of the scientists on the study. Keeping the temperature increase that small will require aggressive mitigation, he said.

If the Earth stays on its current course without reversing greenhouse gas emissions, and global temperatures rise 5 degrees Celsius, as scientists say is possible, the pace of change will be at least 50 times and possibly 100 times swifter than what's occurred in the past, Field said. The numbers are imprecise because the comparison is to an era 55 million years ago, he said.

"The planet has not experienced changes this rapid in 65 million years," Field said. "Humans have never seen anything like this."

Field, in the school's Department of Global Ecology with the Carnegie Institution for Science, and Noah Diffenbaugh, an associate professor of environmental Earth system science, reviewed and synthesized existing research on climate change for a special issue of Science: "Natural Systems in Changing Climates."

They looked at climate events or major transitions that have happened on Earth since the extinction of the dinosaurs. Those include the period when the Earth emerged from an ice age. Temperatures then increased between 3 and 5 degrees Celsius, similar to the amount scientists say is possible with ongoing climate change. But that change happened over about 20,000 years, the scientists said, and not decades as is happening now.

They also looked at a period when global temperatures dropped 11 to 12 degrees over a period 52 million to 34 million years ago.

"That's a larger change in global temperature than what's likely to occur over the next century, but it happened over 18 million years," Diffenbaugh said. "So it was a high-magnitude but relatively low-rate event.

"We find periods of Earth's history where the global temperature change was of similar magnitude, but the rate was an order of magnitude slower."

Ecosystems shifting a yard a day
The changes that are expected ahead will happen much faster than the rate at which species and ecosystems typically are able to adjust, Field said.

Plants and animals essentially would need to move about 1 yard each day farther north or higher in elevation to maintain the conditions they prefer, Field said. While farmers and others can shift where they grow crops, Field said, it's different for a butterfly or a maple tree.

"Maple trees are not good at moving," Field said, adding, "You don't have forests moving over long distances very, very fast."

Trees can shift over time when seeds are blown and squirrels carry acorns, but it typically is not that rapid, he said. The fastest that trees have had to move in the past was tens of meters per year. That's known from pollen records, he said.

"We actually don't have any good examples of them moving as fast as they'll need to in the future because the climate zones haven't moved that fast," Field said.

At the same time, species and plants will be affected by other human-induced changes, the paper said.

"In responding to those rapid changes in climate, organisms will encounter a highly fragmented landscape that is dominated by a broad range of human influences," the study said. "The combination of high climate-change velocity and multidimensional human fragmentation will present terrestrial ecosystems with an environment that is unprecedented in recent evolutionary history."

Mitigation, adaptation needed
The rapid pace of climate change, Field said, "really sets a schedule by which adaptation changes need to be made." That includes such moves as flood protection and building different kinds of structures.

Some of the changes to the planet cannot be stopped because the temperature increase is unavoidable. But the scientists emphasized that people do have the ability to affect the severity of the shifts.

To hold the temperature increase to about 1.5 degrees, the globe would need to cut its greenhouse gas emissions to zero by 2050, and then have negative emissions, meaning "the sum of all human activities is a net removal of CO2 from the atmosphere," the study says. If that happens, changes by the end of the century will be less severe, Field said.

But it will require transitioning away from fossil-fuel-based infrastructure over the next few decades, he said. If fossil fuels are burned after that, he said, it will have to be with the capture of carbon pollution.

There are many obstacles to this outcome, the Stanford paper says.

"Demand for energy-enabled improvement in human well-being creates additional inertia, particularly given that 1.3 billion people currently lack reliable access to electricity, and 2.6 billion people rely on biomass for cooking," it says. "The political process provides further inertia, both because emissions continue as political negotiations take place and because mitigation proposals are built around gradual emissions reductions that guarantee further emissions even if such proposals are eventually adopted."

If greenhouse gases are removed and temperatures rise less, that will only shrink the pace of change.

"Even with aggressive mitigation, the changes are substantial," Field said, "and they're still very fast."